New technologies could make it possible to bring extinct species back to life, concludes a paper published on April 4 in the journal Science. These advances include back-breeding (assembling or reassembling an extinct species' genes), cloning and genetic engineering.
Woolly Mammoth
A leading candidate for de-extinction is the woolly mammoth. Russian scientist Semyon Grigoriev, of the Sakha Republic's mammoth museum, plans to replace the nuclei of an elephant egg with nuclei extracted from woolly mammoth bone marrow. The elephant would theoretically become a surrogate mother to a baby mammoth.

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View Caption+#2: Tasmanian Tiger

Tasmanian tigers died out in 1936, in part because they had little genetic diversity which translates to "bad news for a species," said Katherine Belov, professor of comparative genomics at the University of Sydney. "Species are less able to adapt to change." Even if Tasmanian tigers -- or other animals -- are resurrected, it will take some time to build up diversity again.

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View Caption+#3: Passenger Pigeon

Experts believe billions of these birds populated the Americas when Europeans arrived. Loss of habitat and commercial exploitation of the birds for their meat are thought to have killed them all off.
Efforts are now underway to revive the species by extracting DNA fragments from preserved specimens, and later, using band-tailed pigeons as surrogate parents.

Louis Agassiz Fuertes, Wikimedia Commons

View Caption+#4: Pyrenean Ibex

The Pyrenean ibex, a horned mammal once common in Europe, was one of the first subspecies targeted for de-extinction. Scientists began the attempts in late 1990s, when the last female Pyrenean ibex was still alive. Even if researchers could successfully clone that individual, there would be no males for her to breed with. Instead, genetic engineering might be required.

Joseph Wolf, Wikimedia Commons

View Caption+#5: Saber-toothed Cat

Since saber-toothed cat bodies are sometimes found frozen, it might be possible to extract preserved DNA and clone the animal. About 5 years ago, scientists did just that with a mouse that was dead and frozen for 16 years. Woolly mammoth remains are also sometimes found in a well-preserved, frozen state.

Cicero Moraes, Wikimedia Commons

View Caption+#6: Dodo Bird

The dodo, a flightless bird, proved to be a tasty meal for humans and other predators. In 2007, scientists found a remarkably well-preserved dodo in a cave. Dodo DNA could be used to resurrect this avian species.

Oxford Museum of Natural History, Wikimedia Commons

View Caption+#7: Ground Sloth

Ground sloths, relatively slow, lumbering animals, were easy targets for prehistoric big-game hunters. Scientists have found remains that still bear soft tissue. As with woolly mammoths, there's a chance extracted DNA could be used to back-breed or clone the large sloths.

University of Texas at Austin, Wikimedia Commons

View Caption+#8:

Irish Elk The Irish elk has been extinct for 11,000 years. Like the woolly mammoth, it inhabited colder regions. As a result, bodies are sometimes found frozen and in relatively good condition, making them candidates for DNA extraction.

Charles Knight, Wikimedia Commons

View Caption+#9: Neanderthal

Earlier this year, Harvard geneticist George Church -- with tongue in cheek -- said that he was seeing an "adventurous female human" to be a surrogate mother to a cloned Neanderthal. While Church was really just theorizing about what it would take to bring a Neanderthal back to life, the possibility could be a reality, should any scientist undertake such a controversial project.

UNiesert, Wikimedia Commons

View Caption+#10: Dinosaur

Paleontologist Jack Horner is leading a project to create a dinosaur out of a chicken -- a "dinochicken." He told Discovery News that birds "are dinosaurs, so technically we're making a dinosaur out of a dinosaur." He and his colleagues have been genetically engineering chickens to reactivate ancestral traits, such as long tails, which are more associated with non-avian dinosaurs.

"We were lucky to have him doing this work, because it would have been relatively easy to dismiss the fossil," Bolet said. The skull is surrounded by a concretion of carbonate rock that has hardened around it like cement.

Although it can't be shown as the direct cause, global warming like we're experiencing now has taken place during past mass extinctions.

Saul Gravy/Getty Images

Fortunately, Bolet said, Méndez "immediately realized that what he had found was a small vertebrate skull, a rather exceptional finding, because screen-washing techniques mostly retrieve disarticulated bones and isolated teeth."

The researchers were used to working with tiny fossils, even ones less than a half-inch across, like this one. But removing the rock crust from the fossilized bone would be impossible without damaging the skull inside, they knew. So they turned to technology. Using computed tomography (CT) scanning, the same sort of imaging used in hospitals, the researchers created a virtual reconstruction of the bone still locked in the rock.

The result, Bolet said, is a three-dimensional digital model that allows the researchers to study the skull. They realized the specimen, which measured only 0.23 inches (5.8 mm) at its widest spot and had 20 teeth, was a previously unknown species. They dubbed the animal Blanus mendezi in honor of the technician who discovered the skull.

B. mendezi dates back to the Miocene epoch and is about 11.6 million years old, but its skull looked very similar to those of worm lizards alive today. The researchers suspect this species lived after the evolutionary split between eastern and western Mediterranean worm lizards, and represents the oldest known record of the western group.

The study also highlighted the mystery of worm lizards, Bolet said — even modern species.

"One of the things that became evident during this study was that the osteology of even living species of Blanus is still not well-known," he said. "At the same time, this precludes a proper identification of fossil specimens at the species level, because variation within species has been barely studied."

Ongoing research will need to focus on describing the bones of both fossil and modern blanids, Bolet said, in order to build a family tree for these wiggling enigmas.